In battery technology, lithium ion technology is used in a wide field of use. Lithium ion battery cells are electrochemical elements which have at least one positive electrode and at least one negative electrode having an intercalation structure into/from which lithium ions can be reversibly intercalated or deintercalated. Intercalation occurs during the charging process of the battery cell and deintercalation occurs during discharge of the battery cell in order to supply current to electrical appliances, where a permissible voltage range is essentially from a minimum discharging voltage of 2.5 V and a maximum charging voltage of 4.2 V. The electrodes are preferably configured with thin walls as metal foil or as metallic mesh structure.
One embodiment of a battery cell and in particular a lithium ion battery cell comprises a metallic housing in which active battery cell components and electrolyte are accommodated. Here, active battery cell components encompass an electrode assembly in which electrodes are arranged in more than two layers in a cross section. Such an electrode assembly preferably has film layers composed of electrochemically active materials (electrodes), conductive materials (current collectors) and separating materials (separators) which can be configured in the (illustrative) form of, for example, jelly rolls in a rolled arrangement or superposed in the form of stacks.
For exchange of the lithium ions to occur in chemical redox reactions the presence of an electrolyte which is introduced into the housing and is, in particular, absorbed by a separator membrane is necessary. In general, the electrolyte comprises a lithium ion electrolyte salt, preferably lithium hexafluorophosphate (LiPF6), dissolved in a water-free solvent, for example ethylene carbonate or dimethyl carbonate.
The behavior of the respective battery cells or a battery pack assembled therefrom in the event of electrical overstressing, for example in the case of overcharging, under thermal stress, in particular at excessive cell temperatures, in the case of mechanical overstressing, e.g. in the case of damage to the cell housing or in the case of an unintended short circuit, for example due to a malfunction, is critical in lithium ion technology. Here, overheating can occur in the battery cell, which may lead to the metallic lithium depositing at the anode. Furthermore, cathode decomposition with liberation of strong oxidants can occur and bring about a vigorous exothermic reaction in the electrolyte. In this case, hot gases which increase the pressure in the interior of the battery cell are evolved, and an uncontrolled temperature increase and possibly burning and even explosion of the battery cell can occur (thermal runaway).
DE 10 2011 120 879 A1 discloses a method for operating a battery, in which when a critical state of a battery comprising a plurality of battery cells is detected, a reaction material is liberated in the interior of at least one single cell by means of a battery monitoring unit, bringing about a decrease in voltage within the at least one single cell or an increase in the internal resistance of the at least one single cell. The battery monitoring unit, which is coupled to a collision sensor system and/or deformation sensor system and, for example, detects severe mechanical damage and/or abnormal positional changes in the battery, determines a functional parameter which measures a charging and/or discharging state and/or an age and/or a degree of damage to the battery or to the single cell. The reaction material can be introduced from the outside or is kept in stock in a vessel which can be opened in a targeted manner by means of electric power, heat, pressure and/or high frequency. The reaction material can contain substances which increase the viscosity of the electrolyte.
Furthermore, it is known from DE 10 2010 054 778 A1 to add further additives which improve the cycling stability and/or operational safety to an electrolyte which is used in a secondary lithium ion cell and consists of an electrolyte salt dissolved in one or more solvents. In this context, mention is made of chelating agents which can form complexes with metal cations which can be released from the positive electrode. Crown ethers, cryptands or spherands, inter alia, which capture undesirable metal cations and immobilize them in order to prevent the migration of such metal cations through the electrolyte solution, with the lithium ions being at the same time adversely affected to only a small extent, are known.